Water-based polymer dispersions are finding favor in many markets, not only because they provide performance similar to that obtained from conventional organic solvent-based products, but also because they are leading a worldwide movement toward the use of more environmentally friendly products. Generally, water-based polyurethane dispersions offer a variety of advantages, including ease-of-handling, nonflammability, and low toxicity, as well as premium performance. Thus, they are of interest for use in a wide variety of markets. It would be desirable to use them, for example, as make and/or size coatings for coated abrasive articles and antislip products (often referred to as friction surface sheet materials and nonskid sheet materials).
Typically, polyurethane dispersions are alkaline and stabilized such that the polyurethane particles do not agglomerate and/or settle out of the water. This can be done, for example, by neutralizing dispersed polymer acid moieties, such as pendant carboxylic acid moieties, with a basic compound such as ammonia or an amine, e.g., triethylamine. Coatings prepared from many such dispersions generally require the addition of one or more coalescing agents, typically coalescent solvents or "cosolvents," to allow the formation of a useful film upon drying. Glycol ethers, such as alkyl ethers of ethylene or propylene glycol, have been successfully employed as cosolvents in such applications. However, the use of coalescing organic solvents in water-based systems increases the concentration of undesirable volatile organic compounds (VOCs).
Prior to the present invention, urethane/acrylic copolymers have been used in water-based curable coating compositions, but not without the use of undesirable amounts of a VOC coalescing agent. A "volatile organic compound" or "VOC," as used herein, is an organic compound that has a vapor pressure of at least 0.1 mm Hg at 20.degree. C. Under this definition, ethylene glycol monobutyl ether (available from Union Carbide, Danbury, Conn., under the trade designation butyl "Cellosolve"), diethylene glycol monoethyl ether (available from Union Carbide under the trade designation "Carbitol"), propylene glycol n-butyl ether (available from ARCO Chemicals, Newtown Square, Pa., under the trade designation "Arcosolve" PNB), and dipropylene glycol n-butyl ether (available from ARCO Chemicals, under the trade designation "Arcosolve" DPNB), are considered VOCs. Furthermore, relatively large amounts (e.g., about 20% by weight (wt-%) or greater, based on polymer solids) of such coalescing agents have been typically required for effective film formation. Thus, it would be desirable to develop a coating composition for various applications, including for use as a bond material for the manufacture of abrasive articles and antislip products that contain low levels of VOCs.